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# problem with 5mm leds Answered

i make a 5mm(3.3v) white  6 led series and run it by 5v adapter without any resistor but after running feu hours 1 or 2 leds slowly lost it's brightness and then it's off
i can't understand what is the problem

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## 9 Replies

five leds in series will need a resistor in series and 18v DC..

When 5v is put on a single 3.3v led you are destroying your leds with 1.7 too much voltage that pushes too much current through led and hurts the semiconductor..

You need to put a 68 ohm resistor in series with each led across 5v !

Click the pic to see the whole image..

neelpal (author)2017-11-09

there is defiant (watt like 1/4,1,2,5) what i use????

neelpal (author)2017-11-09

is 68 ohm and 68kilo ohm is (=)

iceng (author)2017-11-10

68 ohm if you want 25 milliamp to light your LED

68Kilo ohm if == 68,000 ohm. Kilo means x 1000

neelpal (author)2017-11-10

thanks.....

iceng (author)2017-11-10

Resistor power = resistor volt x amperes = 1.7 x .025 = .0425 watt.

You can use an 1/8 watt resistor or a 1/4 watt if that is all you have on hand.

rickharris (author)2017-11-08

Limit the current with a resistor.

look up the data sheet for your LED if you can it will tell you the reccomended current.

steveastrouk (author)2017-11-08

You have to put a resistor in series with them.

Downunder35m (author)2017-11-08

With those specs there is no chance the LED's would turn on on 5V if connected in series.
I guess you connected them in parallel.
This would explain them going dim and dead as they burnt out from the overload.
It is always advised to use the right resistors to limit the current the LED(s) can get.